Theresa Collins lives next to a park, but her kids don't play there all that often. For one thing, all three of her children lead busy lives, what with school, piano lessons, soccer practice and the constant distraction of the home computer. What's more, she fears that the park is dangerous. "I've heard of people exposing themselves there," says Theresa, a 42-year-old special-education teacher in Sarasota, Fla. And while she's not sure if the scary stories are true, she would rather be safe than sorry, like so many other contemporary parents. Her daughter Erica, 9, isn't allowed to visit the park without her brother Christopher, 11, who wasn't permitted to play alone there until about a month ago. As for Matthew, 16, who might have supervised Christopher, he avoids the park by choice. He favors video games. "It's a shame," says Theresa. So why doesn't she take the kids to the park? "It's boring. And I don't have time," she says. "When I'm home, I have a lot to do here."

No wonder America's swing sets are feeling lonely. With so many roving flashers to elude, so many high-tech skills to master, so many crucial tests to pass and so many anxious parents to reassure, children seem to be playing less and less these days. Even hassled grownups are starting to notice. "We're taking away childhood," says Dorothy Sluss, a professor of early-childhood education at East Tennessee State University. "We don't value play in our society. It has become a four-letter word."

Statistics back her up. In 1981, according to University of Michigan researchers, the average school-age child had 40% of the day for free time  meaning hours left over after sleeping, eating, studying and engaging in organized activities. By 1997, the figure was down to 25%.

The very existence of research studies on play suggests that ours is a serious society that can take the fun out of almost anything, including the issue of fun itself. That's why any list of the enemies of play must begin with adults, who make the rules. If play is endangered, it's parents who have endangered it, particularly those who feel that less goofing off in the name of youthful achievement is a good thing. See Dick run. Well, that's fine for little Dick, but wouldn't most parents rather raise a Jane who sits still, studies and gets into Harvard?

If so, they're shortsighted, say the experts on play. Alvin Rosenfeld, co-author of The Over-Scheduled Child: Avoiding the Hyper-Parenting Trap, holds an old-fashioned view of play: it's joyful and emotionally nourishing. Stuart Brown, a retired psychiatrist and founder of the Institute for Play in Carmel Valley, Calif., believes that too little play may have a dark side. What Brown calls "play deprivation" can lead, he says, to depression, hostility and the loss of "the things that make us human beings."

Play doesn't just make kids happy, healthy and human. It may also make them smarter, says Rosenfeld. Today's mania for raising young Einsteins, he observes, might have destroyed the real Einstein  a notorious dreamer who earned poor grades in school but somewhere in his frolics divined the formula for the relationship between matter and energy. Play refreshes and stimulates the mind, it seems. And "frequent breaks may actually make kids more interested in learning," according to Rhonda Clements, a Hofstra University professor of physical education.

The case for play is simple and intuitive, which is what makes the decline of play a mystery. If Dick can run wild and get into Princeton too, then why isn't he out there running his little head off? That play has real value won't surprise most parents. That their kid horses around less than they did when they were young probably doesn't shock them either. The puzzle is, Where did all the playtime go?

Millie Wilcox, 60, thinks she knows. The retired nurse and mother of two grown boys (one of them being this writer) doesn't have a Ph.D. in child psychology, just a memory of her own Ohio childhood picking elderberries in the alley and once  imagine doing this today  playing house inside a cardboard box set smack dab in the middle of the street. "There wasn't so much traffic back then," says Wilcox, "and it seems like every neighborhood had a vacant lot. Vacant lots were important. Plus, our mothers were around during the day, and they knew everyone on the block, so they weren't scared for us."

There's common sense behind Wilcox's nostalgia for her old stamping grounds. After all, play needs to happen somewhere  preferably somewhere safe and open and not entirely dominated by grownups  but those idyllic somewheres are growing scarce. "In the huge rush to build shopping malls and banks," says Clements, "no one is thinking about where kids can play. That doesn't generate tax revenue."

What about those inviting vacant lots? "There's practically no such thing anymore," laments urban planner Robin Moore, a former president of the International Association for the Child's Right to Play. Thanks to sidewalk-free subdivisions, congested roads and ubiquitous commercial developments, "all the free space has been spoken for," says Moore. Roger Hart, an environmental psychologist at the City University of New York, cites a general "disinvestment in public space" as one reason children are playing less outdoors. Even public sandboxes are vanishing. Says Hart: "People have become paranoid about animal waste." What's more, as the average family size gets smaller and suburban houses are built farther apart, "kids have a harder time finding each other than they used to," Moore says.

Parental fear is also a factor. Fear of molesters, bacteria, zooming suvs. Neighbors who own guns. Neighbors who let their kids eat refined sugar. The list is as lengthy as last Sunday's newspaper, and it grows longer with every new edition. "It used to be," Hart says, "that in the presence of one another, kids formed a critical mass to keep each other safe. Gone are the days when children make any of their own plans." Their fearful, ambitious parents made plans for them, but these plans don't always mesh, unfortunately. A suburban Chicago mom who wishes to remain anonymous called up a school friend of her daughter's to arrange a play date. The kindergartner was booked solid. "It seems like kids today are always on the way to somewhere," complains the disillusioned mom.